status:

Spiny burr grasses (Cenchrus incertus and Cenchrus longispinus) are listed as noxious in class 4 in Cooma-Monaro, Snowy River and Southern Slopes LCAs in the Southern Tablelands and South East Region.

Description

Two very similar erect to spreading annual grasses to 60cm high. Stems are branching and may root if they contact the soil. Leaves are up to 20cm long and 5-8mm wide, flat and hairless but finely serrated. Narrow linear seed head carry up to 40 green to straw-coloured burrs. Burrs have 11-43 spines (C. incertus) or over 40 spines (C. longispinus) and contain 1-3 seeds.

These weeds prefer disturbed sites on sandy infertile soils. The burrs reduce the value of wool and hides and make affected animals unpleasant to handle. They can cause ulcers in the mouth of stock.

Dispersal

Burrs cling to animals, clothing, vehicle tyres and machinery. They may also be spread in contaminated hay.

Look-alikes

The burrs are quite distinctive. The lush appearance of the plant prior to flowering is also quite unlike native grasses of the tablelands.

On the south coast there is a native species, hillside burr grass (Cenchrus caliculatus), which often grows on rocky slopes with a warm northerly aspect. It also has quite broad bright green leaves, and looks similar to kikuyu (Pennisetum clandestinum) until it produces its spikes of black burrs in late summer. This grass can develop into extensive patches. It is very common in parts of the Brogo area of the Bega Valley. Unpleasant though it may be to walk through, it is not a weed. It often occurs in areas which are too steep for farming so is not often a problem for livestock.

Another burr producing plant is cat's head or caltrop (Tribulus terrestris). It is not a grass, but a low, mat-forming herb with divided leaves and small yellow flowers, which are followed by spiny burrs. These are very easy to transport around in the soles of shoes, or on animals or vehicles. However, it is not listed as noxious on the Southern Tablelands or South Coast.

Control

Dig or spot spray weedy burr grasses before seeding. Seed is short-lived in the soil so prevention of seeding for 3 years can eradicate this weed. Once a dense infestation has developed, cultivation and establishment of a vigorous perennial pasture may be needed, but may be difficult on the poor soils this weed prefers. Not very competitive in pasture, particularly lucerne.